I have read that Satan and his cohorts were tinkering with the gene pool before the flood. What made them stop tinkering after the flood? Or did they?
There’s Biblical evidence that his tinkering continued after the flood. The Israelites encountered Nephilim when they entered the Promised Land. (Numbers 13:31-33) And some believe that the UFO sightings in our lifetimes indicate a return of the Nephilim in the last days.